In many laser beam systems, particularly those using high power lasers, the laser beams acquire poor spatial profiles because of distortions introduced as the beams are directed through chains of optical devices. In general, spatially distorted laser beams must be "cleaned" before they can be used effectively in linear or nonlinear optical systems. One prior method of laser beam clean-up uses a pinhole at a Fourier plane to filter out the high spatial frequency components. Such pinholes, which are approximately 10 microns in diameter for visible wavelengths of light, must be very thin, however, and therefore cannot withstand high power laser beams.
A desirable aspect of spatial filtering for laser beam clean-up is that a cleaned laser beam retains the same temporal characteristics as the distorted beam. A recent improvement of this filtering concept uses photorefractive two-beam coupling for better energy efficiency. However, current methods of laser beam clean-up using photorefractive two-beam coupling also require a pinhole. Thus, for removing spatial distortions from high power laser beams, there is a need for a method that is energy efficient, that retains the temporal characteristics of the distorted beam, and that is not subject to the damage and misalignment problems caused by pinhole filters.